US: New launch attempt on Saturday for Nasa's Moon rocket

Nasa will make a second attempt to launch its powerful new Moon rocket — on Saturday — after scrubbing a test flight earlier this week, an official said on Tuesday.

The highly anticipated uncrewed mission — dubbed Artemis 1 — will bring the United States a step closer to returning astronauts to the Moon, five decades after humans last walked on the lunar surface.

Mission manager Mike Sarafin declared that the Nasa team "agreed to move our launch date to Saturday, September the third".

The blastoff had been planned for Monday morning, but was cancelled because a test to get one of the rocket's four RS-25 engines to the proper temperature range for launch was not successful.

Sarafin announced the date for the new launch attempt during a media briefing on Tuesday, and Nasa later tweeted that the two-hour launch window on Saturday would begin at 2.17pm local time (18.17 GMT).

Launch weather officer Mark Burger said that there was a 60 per cent chance of rain or thunderstorms on the day of the launch. Yet, he added that there was still a "pretty good opportunity weather-wise to launch on Saturday''.

The goal of Artemis 1, named after the twin sister of Apollo, is to test the 98-metre-long Space Launch System rocket, as well as the Orion crew capsule that sits on top of it.

Mannequins equipped with sensors are standing in for astronauts on the mission, and will record acceleration, vibration and radiation levels.

Tens of thousands of people — including US Vice President Kamala Harris — had gathered to watch the launch, 50 years after Apollo 17 astronauts last set foot on the Moon.

Ahead of the planned launch on Monday, operations to fill the orange-and-white rocket with ultra-cold liquid hydrogen and oxygen were briefly delayed by a risk of lightning.

A potential leak was detected during the filling of the main stage with hydrogen, causing a pause. After tests, the flow resumed.

Nasa engineers later detected the engine temperature problem and decided to scrub the launch.

"The way the sensor is behaving ... doesn't line up with the physics of the situation," said John Honeycutt, manager of the Space Launch System program, adding that such issues with sensors were "not terribly unusual".

Sarafin said the team would reconvene on Thursday to assess the situation.

The Orion capsule is to orbit the Moon to see if the vessel is safe for people in the near future. At some point, Artemis aims to put a woman and a person of colour on the Moon for the first time.

During the 42-day trip, Orion will follow an elliptical course around the Moon, coming within 100km at its closest approach, and about 64,373km at its farthest — the deepest into space by a craft designed to carry humans.

One of the main objectives is to test the capsule's heat shield, which, at 4.87m in diameter, is the largest ever built.

Gateway would serve as a staging and refuelling station for a voyage to the Red Planet, which would take a minimum of several months.